A nation that just stepped back from the brink of conflict with Syria paused Wednesday to honor and reflect on the nearly 3,000 victims of 9/11, the day terrorist attacks spurred two other long-running conflicts in the Middle East.

In New York, hundreds of friends and families of the victims stood silently - many holding photos of their loved ones - as bagpipes played. Relatives recited the names of those killed when two hijacked commercial airliners slammed into the World Trade Center's Twin Towers. Another plane that day crashed into the Pentagon near Washington, and a fourth plunged into a field near Shanksville, Pa.

President Obama marked the anniversary with a moment of silence on the South Lawn of the White House, along with first lady Michelle Obama, Vice President Biden and wife Jill Biden. They walked out of the White House at 8:46 a.m. ET, the moment the first plane hit the World Trade Center tower. Bowing their heads in a moment of silence, they were followed by a bugler playing taps.

Obama attended a Pentagon ceremony later Wednesday morning, quoting the Bible, noting the resilience of victims' families and saluting those who served in the military and launched public service projects on behalf of 9/11 victims. A huge American flag draped the building near the spot where a hijacked jet struck at 9:37 a.m., killing 184 people.

While Obama did not directly address the Syrian crisis at the Pentagon ceremony, he vowed to defend the nation against potential threats.

"Let us have the strength to face the threats that endure, different though they may be from 12 years ago, so that as long as there are those who would strike our citizens, we will stand vigilant and defend our nation," he said.

A stronger police and security presence was apparent in New York and Washington, as it has been on past 9/11 anniversaries. Security was also beefed up at several embassies, according to State Department officials.

In a speech to the nation Tuesday night, Obama made a case for military strikes at the regime of Syrian President Bashar Assad, invoking the image of hundreds gassed by chemical weapons. But the president said action would be delayed while a diplomatic resolution was being pursued.

In New York, one of those reading the names of victims

put out a plea to the president to avoid conflict with Syria. "Please don't bring us to another war," said the woman, who was honoring her late uncle, Jose Manuel Cardona.

Other relatives focused on the solemness of the day.

Denise Matuza, 46, from Staten Island, lost her husband, Walter, on 9/11. She plans to return to the memorial ceremony each Sept. 11. "We'll still keep coming back," she said, as her 21-year-old son, also named Walter, and two other sons stood nearby.

Outside Shanksville, dozens of relatives of those who perished aboard United Flight 93 gathered at the crash site.

"This allows us to reconnect with each other and share the day together and the sorrow," said Gordon Felt, who lost his brother Ed. "We reignite the memories of that day, so that we don't forget what happened."

Alice Hoagland, whose son, Mark Bingham was on United Flight 93, agreed that the anniversary serves a purpose. "I dread the day but I also welcome it, because we reconnect and because it's easier to be sad with other people who are, too," she said.

Hoagland was one of thousands around the nation who volunteered to work on projects as part of a 9/11 National Day of Service, a campaign launched in 2002 by victims' relatives and supporters.

"It helped turn around 9/11 for me," by making the anniversary a more positive occasion, said Hoagland, who planned to help fix up a fire training facility.

The Pennsylvania observance was low-key compared with recent years. The event was attended by Michelle Obama in 2010, by the president on the 10th anniversary in 2011 and by Vice President Biden last year.

Interior Secretary Sally Jewell started to cry toward the end of her remarks as she recalled a service at the national memorial the previous evening at which jet entrails appeared in the sky overhead.

"It was very powerful." Jewell said, choking up. She struggled to complete her speech and received a standing ovation when she did.

There were several milestones for the families to applaud: Ground was broken Tuesday for the memorial visitors center, and a National Park Service charity announced that $40 million had been raised to finish the building the memorial.

For many here, it was a day when sorrow was mitigated by pride -- in the memorial that's taken shape.

"In some ways this feels like the first year we came here," said Larry Catuzzi, whose daughter, Lauren, was on the flight. "But I'm so proud of what we've done to create this memorial."

Actor Gary Sinise, a longtime supporter of the military and disabled veterans, played an afternoon concert and barbecue with his Lt. Dan Band at Fort Belvoir, Va., on behalf of the military and their families.

"I wanted to do something special on Sept. 11,'' Sinise told USA TODAY. "Every year at this time, I feel a powerful urgency to make sure we pay tribute and respect to the military and first responders."

Sinise, who routinely holds concerts to benefit wounded veterans, says as years go by, the immediacy of 9/11 may diminish. "I'm around military and first responders who remember it like it was yesterday,'' he says. " But I always feel a very powerful urgency to make sure we pay tribute and respect. Sept. 11 was a powerful wake up and a powerful life-changing event for me and so many people I know."

At New York's memorial, a small crowd gathered by 8 a.m. Some people invited to the memorial - which contained a much smaller group of attendees than this time during last year's anniversary - hugged and kissed each other. Others held photos of their loved one who had perished.

One woman wore a shirt that was emblazoned with the image of a woman's face. "We love & miss you" it said.

As she has done in years' past, Kent Place School teacher Reba Petraitis will have a special lesson about remembrance and memorials on Wednesday. Since the majority of her 12th graders at the Summit, N.J., school don't have clear memories of 9/11, Petraitis tells them to think about another loss that affected them, such as the death of a grandparent, and then talk about the need to memorialize others.

"It's really a highly emotional lesson," Petraitis said.

For most of those students, "Sept. 11 is history â?? they don't remember it," she said. "I also ask them to go home and ask their parents what are their memories of the day to foster family discussions."

Throughout the school year, Petraitis and her students also discuss domestic and international terrorism, school shootings, what makes someone decide to become a terrorist and what students can do "to make this world a better place to live."

The class is a senior elective on contemporary history, she said, but it has a large focus on terrorism and 9/11.

She noted that as time goes on, the attacks will become "more history than a living event."

But "as long as there are museums and memorials, then there are reminders" of Sept. 11, 2001, she said. "And that's the reason for the memorials."